The percentage of Americans who get their news via Facebook and other social networks has doubled in the past two years, a trend that makes traditional TV news and print newspapers even more vulnerable to losing their audiences, a new study says.

A poll conducted in May and June showed about 19 percent of adults in the United States said they saw news or news headlines on a social-networking site the previous day, compared with just 9 percent in 2010, according to the Pew Research Center.

That trend cuts across almost all age and racial demographics, but is particularly apparent in adults under 30: Almost as many people learned about news the previous day on a social-networking site (33 percent) as on TV (34 percent), while only 13 percent read it in either the printed or digital versions of a newspaper.

"The transformation of the nation's news landscape has already taken a heavy toll on print news sources, particularly print newspapers," the report said. "But there are now signs that television news - which so far has held onto its audience through the rise of the Internet - also is increasingly vulnerable, as it may be losing its hold on the next generation of news consumers."

About 55 percent said they watched a TV news program the day before they were polled. But among adults younger than 30, only 34 percent had watched a TV news program the previous day, down from 49 percent in 2006.

And just 23 percent said they read a print newspaper, a slight drop from the 26 percent recorded in 2010, but a larger decline compared with 47 percent who did so in 2000.

Phones and tablets

Mobile devices such as smartphones and tablets are reshaping how people get news. The percentage of people who learned about news stories online remained at 34 percent between 2010 and 2012.

"However, the percentage who regularly get news on a cell phone, tablet or other mobile device has nearly doubled since 2010, from 9 percent to 15 percent," the report said.

That increase is driven by the rapidly growing portion of people who access the Internet on their mobile devices. In 2012, 55 percent said they went on the Internet through a cell phone, tablet or other mobile devices, compared with 31 percent in 2010.

"The percentage regularly getting news from a social-networking site, such as Facebook, Google Plus or LinkedIn, also has increased dramatically - from just 2 percent in 2008, to 7 percent in 2010 and 20 percent currently," the study said.

And those trends are also affecting the use of search engines for finding news.

"Search engines like Google, Bing or Yahoo continue to be the largest single tool in finding news online, but the substantial growth in their use between 2008 and 2010 has leveled off," the report said.

Twitter's numbers

Twitter, however, has not been as big a beneficiary of the news consumption shift. Previous studies showed only 13 percent of adults ever used Twitter or read tweets.

But the latest Pew study said Twitter "barely registers as a news source," with just 3 percent of the general public saying they regularly got their news through the microblogging service, and 4 percent said they "sometimes get the news there."

Yet, for those who use Twitter, the service is an important news source: 27 percent said they now regularly receive news from reading tweets, up from 17 percent in 2010.

The study relied on a representative sample of about 3,000 adults interviewed by phone and had a margin of error of plus or minus 2.1 percentage points.